L15 Motor Pathways Flashcards
1
Q
- What are the four main components of the cortex involved in the focus, planning/programming, selection and commandment/execution of movements?
A
- Parietal (Par)
- Secondary motor (M2) (includes premotor and supplementary motor)
- Prefrontal (Pf)
- Primary motor (M1)
2
Q
- What would happen in a lesion to the Parietal Cortex?
A
Attention (+ recognition loss)
3
Q
- What would happen in a lesion to the Secondary Motor cortex (M2)?
A
- No complex moves/incoordination/forced grasp reflex
- Posture/tone issues (eg akinesia, spasticity)
4
Q
- What would happen in a lesion to the Prefrontal Cortex?
A
No moral/social (-ve schizophrenia)
5
Q
- What would happen in a lesion to the Primary Motor cortex (M1)?
A
No moves (~corticospinal)
6
Q
- What cortex is located in the precentral gyrus / paracentral lobule and what is its main function?
A
- Primary Motor - M1
- Moves (simple)
7
Q
- What cortex is located in the caudal frontal lobe and what is its main function?
A
- Secondary Motor - M2
- Plan (complex)/imagine
- Posture/tone
8
Q
- What cortex is located in the rostral frontal lobe and what is its main function?
A
- Prefrontal
- Moral/social
9
Q
- What cortex is located in the caudal parietal lobe and what is its main function?
A
- Parietal
- Focus/attention
10
Q
- What are the two types of movement?
A
- Skilled: distal somatic muscles - alpha cells
- Basic: proximal somatic muscles - gamma cells
Detail:
- Skilled - eg finger movement: playing an instrument, writing, combing hair
- Basic - eg gluteus maximus, basic trunk muscles that keep body erect, basic global movements like walking
11
Q
- Describe the nervous control of movement (basic)
A
- The cortex controls everything, with the help of subcortical regions eg thalamus.
- Descending axons from the cortex/BS - synapses in the spinal cord (SC) and will excite an alpha/gamma cell to instigate contraction of the muscle and hence movement.
- Many descending pathways are inhibitory. Inhibitory interneurons will prevent excitation of the postsynaptic cell, eg in the switching off of a reflex.
12
Q
- Describe the BASIC movement pathway.
A
- Medial set
- Features: phylogenetically older, crucial for life
- Function: basic (gross, proximal) movements
- Posture (tone), locomotion
- Balance/equilibrium (vestibulospinal tract)
Main Centres:
-
Brainstem
- Basics: posture/locomotion/balance/equilibrium
- Reticulospinal tract, Vestibulospinal tract (extensors)
-
Hypothalamus
- Emotional expression of basics
- Controls brainstem (as does cortex): hierarchy
- Eg freeze, flight, fright
- Hypothalamoreticular tract, hypothalamospinal tract
Detail
- BS Reticular Formation - reticulospinal
- Also good at locomotion
- Vestibular formation
- Vestibulospinal tract - input from inner ear (macula receptors)
- Once you’ve got a sense you’ve lost balance (from head tilts), the inner ear will send info into the vestibular nuclei and this will fire off to correct balance (very fast)
- Activates extensors (to accommodate re-balance)
- Hypothalamus - “second in command”, the “prince” of the brain
- Emotional expression of mvmt - many of our expressions are through mvmt, eg hand gestures - we can gage how someone feels through movement
- Eg a tiger enters the room will trigger a number of behavioural responses: (i) Could freeze to “avoid detection” (ii) Could flee/fight - these are single responses induced by the hypothalamus
- Hypothalamoreticulo/hypothalamospinal - mixed in with reticulospinal/vestibulospinal tracts
13
Q
- Describe the SKILLED movement pathway. [long response]
A
- Lateral set
- Features: phylogenetically newer, quality of life; superimposes on basic template
- Function: skilled (fine, distal) movement
- Goal-driven, voluntary: “I want to do this”
Corticospinal tract (skilled, learning)
- Motor (M1,2), sensory (S1), higher-order (eg cingulate)
- Layer V (Betz); one cell to one muscle group
- M1 map (homunculus): long white matter path
- Pyramidal decussation:
- Cross (90% = 90% lateral CsT)
- No cross (10% = 10% ventral CsT)
- SC (cervical): ventral (motor: alpha, gamma) horn (+ dorsal horn = gating?)
Rubrospinal Tract (skilled, learnt; helps CsT)
- Red nucleus
- Ventral tegmental area: all cross
- SC: Ventral (motor: alpha, gamma) horns
Detail:
- CsT - the best skilled mover; it drives learning, eg of complex skills. While we learn, the CsT is very active.
- Comes from a number of different cortical areas, not just the motor cortex (M1, M2, primary somatosensory S1, higher-order cortices eg cingulate)
- Axons have their cell bodies in layer 5 of the cortex; the giant cells of Betz.
- Homunculus map (M1) proportional to the density of innervation: long wm paths (corona radiata -> external capsule -> midbrain; cerebral peduncle)
- Motor decussation - most cross in the ventral white commissure and from the lateral CsT, ~10% stay on the same side and form the ventral CsT
- Some terminations in the dorsal horn that originate from the sensory/higher-order areas of cortex which could have something to do with “sensory gating” or focusing attention, eg appreciation of a “nice touch”
- RsT - much larger in animals like rodents; smaller in us
- Involved in skilled movement
- Once the movement is learned by the CsT the RsT will “help” it in the skilled mvmts
- Comes from the red nucleus and synapses on amn’s and to some extent gmn’s
14
Q
- Describe the subcortical areas helping various motor cortices regarding movement.
A
Action - Cortex Involved - Subcortical Help:
- Focus - parietal (caudal) - thalamus (pulvinar)
- Plan/programme - M2 - basal ganglia
- Select - prefrontal - basal ganglia
- Execute - M1 - cerebellum
15
Q
- Describe the involvement of the Parietal Cortex on Movement
A
The caudal areas just behind the postcentral lobe drive focus and attention for movement.
It receives heavy input from 3 major sensory modalities - somatosensory, audition, hearing - and tries to make sense of things in our world.
It asks questions; car keys example: “what is this? What do the keys do? How do they fit into my life? What do they look like?” - It recognises and puts the object into context.
- It is a multi-modal area that combines modalities to make sense and focus attention
Lesions will result in loss of attention, especially in the right lobe (would bump into things on one’s left)
